The invention relates to a system for recycling exhaust gas in an internal combustion engine according to the preamble of the principal claim.
In a system of this kind disclosed in DE 30 34 971 C2 exhaust gases of the internal combustion engine are returned to the intake duct for the internal combustion engine. The connecting duct is here embedded in a heat exchanger for cooling the recycled exhaust gas through a broad range.
Taken in itself, it is also known that the recycled exhaust duct is fastened by a flange with two screws to the air intake tube made of plastic. In order to insulate the exhaust gas duct thermally from the air intake tube, mixture air is fed in the area of the flange by means of a diffuser tube. With this arrangement the exhaust gas temperature can be lowered in the area of the flange from about 450xc2x0 C. to about 125xc2x0 C. at a recycling rate of about 20%.
Thermal peaks occur in such systems, especially in the areas of the gaskets, made of plastic as a rule, at the connection of the duct carrying the returned exhaust gas and in areas lying opposite the air entry opening. It is often difficult, due to the relatively small cross sections and relative long paths, to carry away sufficient heat. In many applications, in connection with direct injection motors, also on account of the exhaust gas return rate to be expected (up to 50%), there is frequently a call for cylinder-selective introduction of the exhaust gas, which leads to additional thermal problems.
The invention is addressed to the problem of improving a system of the kind referred to above such that an optimum lowering of the temperature will be possible.
The system of the invention is advantageously suitable, setting out from the generic kind, for solving the stated problem by the distinctive features of the principal claim. Owing to the fact that a cooling element in the form of a cooling channel for a liquid coolant is placed in a connecting duct for the recycled gas, which is integrated into the flange-like attachment of the duct connecting to the intake tube, the thermal stress on the plastic intake tube can be reduced at high recycling rates by simple means. Also the temperature of the aspirated air in the air intake tube can thereby be positively influenced.
In general, with the system according to the invention the thermal stress of the internal combustion engine, the exhaust temperature, the NOx emission and the fuel consumption are reduced. If the motor coolant is used as the coolant, the result is a simpler and less expensive construction.
The coolant duct can advantageously be integrated into the air intake tube, which as a rule is made of plastic, the transition from the cooling channel into the internal combustion engine being situated in the cylinder head flange of the motor, and the interface being sealed with an additional gasket. Alternatively it is also possible to place a separate coolant line into the flange between the exhaust pipe and the air intake tube, or for the cooling passage also to be placed on a given length into or onto the exhaust pipe. In another embodiment of the invention, the cooling element is a massive heat-conducting part which is a component of the connecting line and is located on the cylinder head in the area of the flange-like connection of the air intake tube. Due to the massive attachment, of the manifold for the recycled exhaust, for example, to the cylinder head, the flowing gases can be cooled simply through the cylinder head flange which has cooling passages anyway.
Advantageously, the elements fastening the intake tube to the cylinder head can be used at least partially as means for fastening the massive part.
It is also advantageously possible to provide a cooling channel carrying coolant in the area of attachment of the massive part in the cylinder head or also at least partially in the massive part, whereby the cooling power can be further optimized.
In another embodiment, the massive heat conducting part is a tubular insert which is integrated internally into the intake tube. This insert is in thermal contact at one end with the cylinder head. With this arrangement, when the intake tube is mounted to the cylinder head a good thermal transfer is easily achieved between the insert, which is preferably made of metal, and the cylinder head. Through this heat transfer the thermal energy delivered by the exhaust gas can be removed into the cooled cylinder head.
This heat transfer can also, if necessary, be increased if the end face of the insert in contact with the cylinder head has an expanded diameter.
The pipe-like connecting duct for the recycled exhaust is brought out through the wall of the intake tube on the side of the insert. The connecting duct and the insert are joined together gas-tight, so that no gaskets are necessary between the connecting duct and the intake tube. The entering exhaust thus strikes against the inside wall of the cooled insert and therefore does not apply any elevated thermal stress to the plastic of the intake tube.
It is especially advantageous if in the area where the connecting duct is brought out there is a gap in the intake tube so as to form a radial space away from the connecting duct and thus to prevent any thermal stress on the intake tube in this area.
These and additional features of preferred embodiments of the invention will be found not only in the claims but also in the description and the drawings, the individual features being applicable individually or severally in the form of subcombinations in the embodiment of the invention and in other fields and may represent advantageous as well as independently patentable embodiments, for which protection is hereby claimed.